Mixer for highly viscous fluids

ABSTRACT

The mixer comprises a tube, one end of which is closed by a stationary piston and the other end by a piston movable in the direction of the tube axis and provided with an axial boring through which a stirrer extends into the tube. The stirrer pivots round its axis and can be shifted in axial direction.

United States Patent Fischer 1 Feb. 11, 1975 MIXER FOR HIGHLY VISCOUS FLUIDS [56] References Cited [75] Inventor: Edgar Fischer, Frankfurt am Main, UNITED STATES PATENTS Germany 2,977,098 3/1961 Watson 259/108 0/1964 Cook [73] Asslgnee. IIoechst Aktlengesellschaft, 3453531 1 Frankfurt am Main7 Germany 3,417,971 12/1968 Blank 259/37 [22] Filed: 1972 Primary Examiner--Robert W. Jenkins 2 303,422 Attorney, Agent, or Firm-Curtis, Morris & Safford [30] Foreign Application Priority Data [57] ABSTRACT Nov. 23, 1971 Germany 2158002 The mix r mprises a tu e. one n of which is closed by a stationary piston and the other end by a [52] U.S. Cl 259/118, 259/ 124, 259/113 piston movable in the direction of the tube axis and [51] Int. Cl B0lf 7/22 provided with an axial boring through which a stirrer [58] Field of Search 259/102, 107, 108, 37, extends into the tube. The stirrer pivots round its axis and can be shifted in axial direction.

3 Claims, 1 Drawing Figure PATENTEU FEB! 1 I975 MIXER FOR HIGHLY VISCOUS FLUIDS The present invention relates to a mixer for highly viscous fluids.

Homogeneous mixing of highly viscous fluids or melts with additives is a procedure frequently carried through for preparing samples in production control or for compounding. This problem does arise, for example, in the manufacture of lacquers, dispersions, ointments, soaps, pastes, dyestuff mixtures, compounds, waxes, plastics, synthetic fibers, and pharmaceutical preparations. The absolute homogeneity of the repective mixture is indispensable for sample evaluation.

All known kneaders are to be filled with the optimum filling amount. With a minor filling amount the mixing effect strongly declines. The kneaders are filled to such an extent that a gas space remains above the material to be mixed. When mixing is effected at elevated temperature, the known kneaders do not ensure protection from oxidation by atmospheric oxygen of the material to be mixed thus the quality of the mixture is often detrimentally affected, for example by discoloration or chemical alteration. It is, therefore, necessary to effect mixing at elevated temperature in this type of kneaders under a protective gas which increases the expenses of the mixing procedure. Moreover, all known kneaders are very complicated mechanical structures which are susceptible to trouble. They have the drawback of relatively long mixing times as the kneading elements cannot be run much faster than corresponds to the free flowing speed of the material to be'mixed. A further disadvantage resides in the fact that kneaders of known type cannot be constructed for small amounts, for example to 50 grams material to be mixed, without considerable expenditure to solve the bearing and tightness problems. Furthermore, emptying and cleaning of the known kneaders is complicated and time consuming. In many cases they have to be disassembled completely for cleaning.

To overcome the aforesaid disadvantages a mixer for highly viscous fluids has been developed comprising a mixing space in the form ofa tube closed at one end by a stationary piston and at the other end by a movable piston which can be displaced in the direction of the tube axis and is provided with an axial boring through which a stirring means extends into the mixing space, said stirring means pivots round its axis and can be shifted in the direction of the said axis.

The mixer of the invention is of simple construction and can be readily heated. The mixed. material can be removed from the mixer equally well either hot or cold and cleaning of the mixer is absolutely uncomplicated. A protective gas need not be used. The mixing time is about one tenth of the mixing time required with known mixers. l 7

The mixer according to the invention will now be described in further detail by way of example with reference to the accompanying drawing.

In a tube 3 the mixing space 7 is shut off by a stationary piston 4 at the one end and a movable piston 5 at the other end which can be displaced in the direction of the tube axis. Piston 5 is provided with an axial boring 8 through which a stirrer 6 extends into the gas space 7, which stirrer pivots. round its axis and can be shifted axially. Tube 3 is placed in an oven 1 with heating 2. Numeral 9 indicates the drive of stirrer 6.

The ratio of diameter to height of the mixing space may vary within relatively wide limits, with lifted stirrer it is in the range of about 5:1 to 1:5. The mixing effect and heat exchange are especially favorable with a ratio of l:l to 1:3. The ratio of the cross sectional areas of the stirring shaft to the annular piston should be in the range of from about 1:1 to 1:10, preferably 1:4 to l:8.

The stirring beam having a circular cross section has a good mixing but no conveying effect. The latter can be obtained, if desired, by beam surfaces with clearance angles. Stirrers with conveying effect exercise, however, a strong influence on the behavior with the stirring motion in axial direction as they promote or hinder the lifting process.

As compared with known kneaders the mixer according to the invention is much easier to operate. By pulling out the movable piston 5 with stirrer 6 the cylindrical mixing space becomes accessible. After the material to be mixed has been filled in, the piston with stirrer is again inserted and thus the mixing space is sealed tightly. When the material to be mixed has reached the desired temperature, the stirrer is set in motion. It moves in two directions, on the one hand, it rotates round the axis of its shaft, and on the other hand, it moves upwards and downwards in the direction of the shaft axis. By this double motion each point of the mixingspace is covered. The movable annular piston moving in opposite direction with respect to the stirring shaft participates in the mixing procedure. Thus during mixing the ratio of height to width of the mixing space permanently varies, which additionally favors the mixing process. The motion in longitudinal direction of annular piston and stirring shaft takes place in a manner such that one part is active while the other part is passive. The respective part becomes active by loading and passive by relief of the load, the downward motion being active and the upward motion passive.

Because of the mixing space being completely filled with the material to be mixed, n0 cavities can occur. The number of revolutions of the stirrer can be considerably increased and mixing can be accelerated. The most favorable number of revolutions is in the range of from 50 to 300 revolutions and 5 to 12 up-and-down strockes of the movable piston per minute. These values and the required driving power strongly depend on the viscosity of the material to be mixed.

When mixing is terminated, stirring is discontinued and stationary piston 4 is removed. By pushing downward piston 5 together with stirrer 6 the mixed material is discharged at the lower end of the tube. It can be molded at once into shaped articles, for example by pressing. After removal of the mixed material, piston 5 together with stirrer 6 are drawn out of the tube and stationary piston 4 is inserted at the lower end of the tube, whereupon the mixer is again ready for use.

What is claimed is:

1 A mixing device for highly viscous fluids comprising a hollow elongated tube having first and second open end portions and defining a mixing space therein, a stationary piston removably mounted in a fixed position closing said first open end portion of the tube and a movable piston slidably mounted in and closing the second open end portion of the tube for movement through said mixing space; said movable piston having an axial bore formed therethrough; and a stirrer having an elongated shaft extending through said bore into said mixing space and having a mixing member thereon in the mixing space; whereby said movable piston is adapted to rest on the material to be mixed in said mixmeans includes means for moving said stirrer axially in said mixing space, said sliding piston maintaining a constant volume in the mixing space by moving vertically in said tube as the volume of the stirrer in the mixing space varies upon reciprocation of the stirrer therein. 

1. A mixing device for highly viscous fluids comprising a hollow elongated tube having first and second open end portions and defining a mixing space therein, a stationary piston removably mounted in a fixed position closing said first open end portion of the tube and a movable piston slidably mounted in and closing the second open end portion of the tube for movement through said mixing space; said movable piston having an axial bore formed therethrough; and a stirrer having an elongated shaft extending through said bore into said mixing space and having a mixing member thereon in the mixing space; whereby said movable piston is adapted to rest on the material to be mixed in said mixing space to maintain a relatively constant volume therein and preveNt formation of gas spaces in the mixing space.
 2. The device as defined in claim 1 including means for rotating said stirrer in said bore.
 3. The device as defined in claim 2 wherein said means includes means for moving said stirrer axially in said mixing space, said sliding piston maintaining a constant volume in the mixing space by moving vertically in said tube as the volume of the stirrer in the mixing space varies upon reciprocation of the stirrer therein. 